The rapid growth of data communications and the deployment of optical communication systems that utilize wavelength division multiplexing (WDM) created a demand for new switching methods. Optical packet switching is considered today a switching method that is particularly suitable for data communications and for optical communication systems that utilize WDM.
There are two main techniques for optical packet switching, and they mainly differ in the structure of optical packets utilized thereby and in switching node operation. The first technique is based on fixed-length packets with synchronous node operation, and the second technique is based on variable-length packets with asynchronous node operation. Variable-length packets are also referred to as bursts and the second technique is also referred to as optical burst switching (OBS).
Basic aspects of the techniques for optical packet switching are described in the following publications:
an article entitled “Architectural and Technological Issues for Future Optical Internet Networks”, by Listanti et al in IEEE Communications Magazine, September 2000, pages 82–92;
an article entitled “IP Over Optical Networks: Architectural Aspects”, by Rajagopalan et al in IEEE Communications Magazine, September 2000, pages 94–102;
an article entitled “Labeled Optical Burst Switching for IP-over-WDM Integration”, by Chunming Qiao in IEEE Communications Magazine, September 2000, pages 104–114; and
an article entitled “Approaches to Optical Internet Packet Switching”, by Hunter et al in IEEE Communications Magazine, September 2000, pages 116–122.
Both techniques of optical packet switching mentioned above have however similar problems that are encountered with bandwidth contention and switching of optical packets that are carried over optical paths at different bit-rates.
Bandwidth contention is defined as contention for a wavelength at the same time among optical packets arriving on a plurality of optical paths. In an optical switch that switches optical packets from a plurality of input paths to a plurality of output paths, bandwidth contention may occur frequently regardless of the switching technique that is used by the optical switch.
The problem encountered with switching of optical packets that are carried over optical paths at different bit-rates is independent of bandwidth contention, and in fact occurs both in a case where there is bandwidth contention and in a case where there is no bandwidth contention. The problem encountered with switching of optical packets that are carried over optical paths at different bit-rates may be appreciated by referring to the following example in which a conventional optical packet switch switches, to a single output path, optical packets that are provided over four input paths.
Considering, for example, a case in which there is no bandwidth contention among any of the optical packets carried over the four input paths, the optical packet switch can place the optical packets from all four input paths serially over the single output path. Typically, the optical packets carried over the output path are equally distributed so that every fourth optical packet originates from the same input path. If all four input paths carry the optical packets at the same input bit-rate of, for example, 10 Gigabit per second (Gbit/sec), an output bit-rate of the optical packets carried over the output path can reach, at best, 10 Gbit/sec.
However, if not all four input paths carry the optical packets at the same input bit-rate, such as when one input path carries optical packets at an input bit-rate of 2.5 Gbit/sec and each of the other three input paths carries optical packets at an input bit-rate of 10 Gbit/sec, an output bit-rate of optical packets carried over the output path can reach, at best, about 5.715 Gbit/sec. It is therefore apparent that in optical packet switching that involves switching of optical packets that are carried over input paths at different bit-rates, overall transmission speed over an output path can be adversely affected even by a single input path that carries optical packets at a low bit-rate. The overall transmission speed over the output path can be even more adversely affected when bandwidth contention is taken into account.
Therefore, techniques that can solve the problems encountered with bandwidth contention and switching of optical packets that are carried over optical paths at different bit-rates may be highly desired.
Some aspects of technologies and related art that may be useful in understanding the present invention are described in the following publications:
an article entitled “Mining the Optical Bandwidth for a Terabit per Second”, by Alan Eli Willner in IEEE Spectrum, April 1997, pages 32–41;
an article entitled “Polarization Insensitive Widely Tunable All-Optical Clock Recovery Based on AM Mode-Locking of a Fiber Ring Laser”, by Wang et al in IEEE Photonics Technology Letters, Vol. 12, No. 2, February 2000, pages 211–213;
an article entitled “Ultra-High-Speed PLL-Type Clock Recovery Circuit Based on All-Optical Gain Modulation in Traveling-Wave Laser Diode Amplifier”, by Kawanishi et al in Journal of Lightwave Technology, Vol. 11, No. 12, December 1993, pages 2123–2129;
an article entitled “Prescaled 6.3 GHz clock recovery from 50 GBit/s TDM optical signal with 50 GHz PLL using four-wave mixing in a traveling-wave laser diode optical amplifier”, by Kamatani et al in Electronics Letters, Vol. 30, No. 10, May 12, 1994, pages 807–809;
an article entitled “Variable optical delay line with diffraction-limited autoalignment” by Klovekorn et al in Applied Optics, Vol. 37, No. 10, Apr. 1, 1998, pages 1903–1904;
an article entitled “Picosecond-Accuracy All-Optical Bit Phase Sensing Using a Nonlinear Optical Loop Mirror”, by Hall et al in IEEE Photonics Technology Letters, Vol. 7, No. 8, August 1995, pages 935–937;
an article entitled “An Ultrafast Variable Optical Delay Technique”, by Hall et al in IEEE Photonics Technology Letters, Vol. 12, No. 2, February 2000, pages 208–210;
an article entitled “Optical switching promises cure for telecommunications logjam”, by Jeff Hecht in Laser Focus World, September 1998, pages 69–72;
an article entitled “Design and Cost Performance of the Multistage WDM-PON Access Networks”, by Maier et al in Journal of Lightwave Technology, Vol. 18, No. 2, February 2000, pages 125–143;
an article entitled “All-optical networks need optical switches”, by Jeff Hecht in Laser Focus World, May 2000, pages 189–196;
a technology brief entitled “Lucent Upgrades Wavestar to 320-Channel, 800-Gb/s Transmission”, in Photonics Spectra, June 2000, page 46;
an article entitled “Record Data Transmission Rate Reported at ECOC 96”, by Paul Mortensen in Laser Focus World, November 1996, pages 40–42;
an article entitled “Multiple Wavelengths Exploit Fiber Capacity”, by Eric J. Lerner in Laser Focus World, July 1997, pages 119–125;
an article entitled “Advances in Dense WDM Push Diode-Laser Design”, by Diana Zankowsky in Laser Focus World, August 1997, pages 167–172;
an article entitled “Multistage Amplifier Provides Gain Across 80 nm”, by Kristin Lewotesky in Laser Focus World, September 1997, pages 22–24;
an article entitled “WDM Local Area Networks”, by Kazovsky et al in IEEE LTS, May 1992, pages 8–15;
an article entitled “Optical Switches Ease Bandwidth Crunch”, by Rien Flipse in EuroPhotonics, August/September 1998, pages 44–45;
an article entitled “Speed Demons: Is ‘Faster’ Better and Cheaper?”, by Stephanie A. Weiss in Photonics Spectra, February 1999, pages 96–102;
an article entitled “Wavelength Lockers Keeps Laser in Line”, by Ed Miskovic in Photonics Spectra, February 1999, pages 104–110;
an article entitled “Optical switches pursue crossconnect markets”, by Hassaun Jones-Bay in Laser Focus World, May 1998, pages 153–162;
a conference review entitled “Optical amplifiers revolutionize communications”, by Gary T. Forrest in Laser Focus World, September 1998, pages 28–32;
an article entitled “Combining gratings and filters reduces WDM channel spacing”, by Pan et al in Optoelectronics World, September 1998, pages S11–S17;
an article entitled “Demand triggers advances in dense WDM components”, by Raymond Nering in Optoelectronics World, September 1998, pages S5–S8;
an article entitled “Optical Networks Seek Reconfigurable Add/Drop Options”, by Hector E. Escobar in Photonics Spectra, December 1998, pages 163–167;
an article entitled “Ultrafast Optical Switch Unveiled”, by Michael D. Wheeler in Photonics Spectra, December 1998, page 42;
an article entitled “Data express Gigabit junction with the next-generation Internet”, by Collins et al in IEEE Spectrum, February 1999, pages 18–25;
an article entitled “Designing Broadband Fiber Optic Communication Systems”, by Juan F. Lam in Communication Systems Design magazine, February 1999, pages 1–4 at http://www.csdmag.com;
an article entitled “Terabit/second-transmission demonstrations make a splash at OFC '96”, in Laser Focus World, April 1996, page 13;
an article entitled “Multigigabit Networks: The Challenge”, by Rolland et al in IEEE LTS, May 1992, pages 16–26;
an article entitled “Direct Detection Lightwave Systems: Why Pay More?”, by Green et al in IEEE LCS, November 1990, pages 36–49;
an article entitled “Photonics in Switching”, by H. Scott Hinton in IEEE LTS, August 1992, pages 26–35;
an article entitled “Advanced Technology for Fiber Optic Subscriber Systems”, by Toba et al in IEEE LTS, November 1992, pages 12–18;
an article entitled “Fiber amplifiers expand network capacities”, by Eric J. Lemer in Laser Focus World, August 1997, pages 85–96;
an article entitled “Technologies for Local-Access Fibering”, by Yukou Mochida in IEEE Communications Magazine, February 1994, pages 64–73;
an article entitled “Wavelength Assignment in Multihop Lightwave Networks”, by Ganz et al in IEEE Transactions on Communications, Vol. 42, No. 7, July 1994, pages 2460–2469;
an article entitled “Wavelength-Division Switching Technology in Photonic Switching Systems”, by Suzuki et al in IEEE International Conference on Communications ICC '90, pages 1125–1129;
an article entitled “Branch-Exchange Sequences for Reconfiguration of Lightwave Networks”, by Labourdette et al in IEEE Transactions on Communications, Vol. 42, No. 10, October 1994, pages 2822–2832;
an article entitled “Use of Delegated Tuning and Forwarding in Wavelength Division Multiple Access Networks”, by Auerbach et al in IEEE Transactions on Communications, Vol. 43, No. 1, January 1995, pages 52–63;
an article entitled “Compact 40 Gbit/s optical demultiplexer using a GaInAsP optical amplifier”, by Ellis et al in Electronics Letters, Vol. 29, No. 24, Nov. 25, 1993, pages 2115–2116;
an article entitled “Bit-Rate Flexible All-Optical Demultiplexing Using a Nonlinear Optical Loop Mirror”, by Patrick et al in Electronics Letters, Vol. 29, No. 8, Apr. 15, 1993, pages 702–703;
an article entitled “All-Optical High Speed Demultiplexing with a Semiconductor Laser Amplifier in a loop Mirror Configuration”, by Eiselt et al in Electronics Letters, Vol. 29, No. 13, Jun. 24, 1993, pages 1167–1168;
an article entitled “Photonic Switches: Fast, but Functional?”, by Daniel C. McCarthy in Photonics Spectra, March 2001, pages 140–150;
U.S. Pat. No. 5,170,273 to Nishio which describes a cross-talk reducing optical switching system which receives electrical digital signals at its input terminal;
U.S. Pat. No. 5,191,457 to Yamazaki that describes a WDM optical communication network in which optical beams are modulated by channel discrimination signals of different frequencies;
U.S. Pat. No. 5,194,977 to Nishio that describes a wavelength division switching system with reduced optical components using optical switches;
U.S. Pat. No. 5,557,439 to Alexander et al. that describes wavelength division multiplexed optical communication systems configured for expansion with additional optical signal channels;
U.S. Pat. No. 5,680,490 to Cohen et al. that describes a comb splitting system which demultiplexes and/or multiplexes a plurality of optical signal channels at various wavelengths;
U.S. Pat. No. 5,712,932 to Alexander et al. that describes reconfigurable wavelength division multiplexed systems which include configurable optical routing systems;
U.S. Pat. Nos. 5,724,167 and 5,739,935 to Sabella that describe an optical cross-connect node architecture that interfaces plural optical fiber input and output links, each link containing plural wavelength channels;
U.S. Pat. No. 5,457,687 to Newman that describes reactive congestion control in an ATM network where the network is formed by the interconnection of nodes each including a forward path for transfer of information from source to destination through the network and a return path for returning congestion control signals;
U.S. Pat. No. 5,774,244 to Tandon et al. that describes an optical communications network that includes a plurality of passive optical networks (PONs) connected in a ring in PON address order, in which communication channels between terminals are wavelength multiplexed;
U.S. Pat. No. 6,233,082 to Johnson that describes an optical transmitter for generating any one of N carrier signals for use in an M-channel WDM system, and
The following chapters in The Communications Handbook, CRC Press & IEEE Press, 1997, Editor-in-Chief Jerry D. Gibson: Chapter 37 on pages 513–528; Chapter 39 on pages 542–553; Chapter 40 on pages 554–564; Chapter 46 on pages 622–649; Chapter 51 on pages 686–700; and Chapter 65 on pages 883–890.
U.S. patent application Ser. No. 09/126,378 of Handelman, now U.S. Pat. No. 6,404,522, describes improvements in communication performance of an optical communication system that communicates data via N different channel wavelengths using WDM.
U.S. patent application Ser. No. 09/389,345 of Handelman, now U.S. Pat. No. 6,574,018, describes a network control system that may be embodied in various elements of a communication network that communicates optical signals multiplexed by WDM. The network control system may limit a number of channel wavelengths actually used for communicating optical signals to an end node, and control and modify data rates carried over channel wavelengths multiplexed by WDM.
U.S. patent application Ser. No. 09/624,983 of Handelman, now U.S. Pat. No. 6,763,191, describes an optical switching apparatus that selectively combines and separates series of optical signal samples using OTDM and/or WDM.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.